The etiology of erectile dysfunction (ED) or impotence, is complex and it is usually divided into the primary or the more frequent secondary dysfunction.
The major cause of ED is vascular but other frequent causes include hormonal disorders, drug use and neurologic disorders.
Treatments for ED can be classified as central or peripheral initiators, central or peripheral conditioners and others. For a comprehensive review of the subject, with discussion on the role of neurotransmitters and neuropeptides, see A. Argiolas and M. R. Melis, Progress in Neurobiology, 47, 235-255 (1995). For classification of treatments, see J. P. W. Heaton et al., Int. J. Impotence Research 9, 115-121(1997).
Among neuropeptides that act centrally to induce penile erection, the best known are ACTH/MSH peptides and oxytocin. These centrally active peptides however are not specific in their action and cannot be used therapeutically because of their important side effects.
Non-peptidyl products are known to be useful for the treatment of ED. Among these, alprostadil (PGE.sub.1) is used topically, and apomorphine and sildenafil are administered by sublingual or oral application. All known agents are not devoid important drawbacks such as emetic properties (apomorphine) and cardiovascular side effects (sildenafil).
A treatment is clearly needed that is as specific as possible, causes a minimum of side effects and is easy to administer.